| One-piece flow and kanban/pull methods have been used to reduce WIP and speed flowtime in manufacturing flow processes; however, these methods have limitations. For example, one-piece flow does not work well when there are relatively large set-up times required between different components. One-piece flow also requires operations to be well-balanced. Unfortunately, these conditions often do not exist. The Theory of Constraints drum-buffer-rope (DBR) method is designed for unbalanced processes, and it has been shown to be effective for products with large operation time variation. However, DBR does not generally optimize flowtime and cannot handle a process with moving constraints (bottlenecks). Recognizing that there are manufacturing applications that have these limitations, we have developed a method called Takt Time Grouping (TTG) for implementing kanban-flow manufacturing when one-piece flow or DBR do not perform well. TTG combines one-piece flow, transfer-batch sizing and DBR concepts through the use of a grouping algorithm. Using a discrete event simulation model, the application of TTG, one-piece flow, DBR and a dynamic version of DBR, that moves the time-buffer and drum when it is known that constraints move (DynDBR), was investigated under varying conditions and production processes. Generalized findings of TTG's advantages over competing methods are presented. |
